There has been a growing trend in recent years for magnetic disk devices to increase in capacity and recording density. The result is a continuing decrease in the size of recording bits formed on the magnetic recording medium. The currently available magnetic recording medium does not readily realize the ultra-high recording density exceeding 3 Gbit/in2 without further reduction in medium noise. Therefore, it is important to make finer crystals constituting the magnetic film. Unfortunately, resulting fine magnetic crystals have such an extremely small volume that they decrease in recording magnetization by the strong influence of thermal energy even at normal temperature. In actuality, information recorded on a low-noise medium with a density of 115 kFCI is attenuated by more than 10% after 96 hours, as reported by Y. Hosoe et al. (IEEE Trans. Magn., 33, pp. 3028–3030, September 1997)
U.S. Pat. No. 5,693,426 discloses a magnetic recording medium which consists of an orientation control layer having the B2 (CsCl) structure and a magnetic layer formed thereon directly or indirectly with a Cr underlayer interposed between them.
Japanese Patent Laid-open No. 21543/1995 discloses a dual underlayer consisting of a first one of Cr and a second one of CrMo alloy. According to this disclosure, the first Cr underlayer is formed directly on the substrate.